The present invention relates to novel dextrins that are highly water soluble, and highly hydratable in a solution which has low free water, at ambient temperature, are viscous relative to a canary dextrin, and are solution stable; the method of preparing them; and their use in a variety of industrial applications.
Starch dextrinization has been known since the early 1800's and may be accomplished by enzyme action, by microbial degradation, by acid hydrolysis, or by heating starch powders either with or without the presence of acid or pH controlling substances (hereinafter "acidifying"). The dextrins formed by heat are known as pyrodexrins and are mixtures of various products of hydrolysis and recombination. Pyrodextrins are generally classified in three groups: white dextrins which are prepared from starch in the presence of an acid catalyst for a relatively short period of time (3-8 hours) at a relatively low temperature (79-120.degree. C.); yellow, or canary, dextrins which are prepared from starch in the presence of an acid catalyst for a more moderate period of time (6-18 hours) at a relatively high temperature (150-220.degree. C.); and British gums which are prepared from starch without any catalyst for long periods of time (10-20 hours) at a relatively high temperature (130-220.degree. C.).
White dextrins and British gums are conventionally up to 95% soluble in water while canary dextrins are conventionally 95 to 100% soluble in water. British gums conventionally form viscous solutions as the name indicates, while white and canary dextrins tend to form relatively less viscous solutions.
The manufacture of pyrodextrins in the dry state is practiced to obtain products which are hydrolyzed or converted to a desired degree and are partially or fully water soluble for a variety of industrial applications. They typically are produced by acidification of the starch, dextrinization, and cooling. In the early stages of dextrinization, hydrolysis is the major reaction due to the presence of high moisture. During the hydrolysis reaction, the molecular weight of the starch is decreased and water is used up. Although some recombination is possible during this phase, recombination is minor until the temperature rises and the water (moisture) level decreases. The hydrolysis process may be accelerated with a catalyst, typically acid.
As the moisture is driven out of the process and temperature continues to increase, the rate of hydrolysis tends to slow down, especially during the latter stages of dextrinization. The processing conditions in the latter stage, namely, high temperature and low moisture, promote recombination of starch molecules which releases water. As recombination occurs, the molecular weight and the branching of the starch increase relative to the hydrolysis product. Further, water is released allowing for further hydrolysis. With time, an equilibrium state is reached between the two reactions, hydrolysis and recombination.
In the traditional dextrinization process, moisture is trapped in the starch bed, particularly in a single phase system, and recombination is in competition with hydrolysis. In a system in which substantially all the free moisture in the system is removed, recombination is in less competition with hydrolysis due to the thorough separation and removal of moisture from the starch. This separation and removal of water results in higher viscosity compositions that still posses all the benefits from the high thermal exposure, particularly high solubility and increased solution stability. Processing dextrins to an anhydrous state is known in the art, producing compositions with a high level of solubility in water at ambient temperatures: however, these tend to be of very low viscosities and/or are not thoroughly hydratable in systems containing little free water, such as in a high solids sugar solution, especially without the addition of heat. There is a need for relatively higher viscosity, thoroughly hydratable dextrin compositions having excellent solution stability characteristics.
Pyrodextrins may be prepared using a variety of equipment, including ribbon agitators, ovens, and fluid bed reactors. Recently, fluid bed reactors have gained favor as better control and reduced time are made possible by the high heat transfer and homogenous mixing characteristic of such equipment.
Dextrinization in fluid bed reactors has been known in the art and produce the same pyrodextrins conventionally known in the art or slight variations thereof. For example, see U.S. Pat. Nos. 2,845,368; 3,967,975; 4,021,927; 4,237,619; and 4,266,348. Further, a variety of processing parameters have been tried. However, many references stress the importance of using moist air, such as U.S. Pat. No. 3,967,975; Canadian Patent No. 1,150,934; and German patent applications DD 157 347 and DD 208 991.
Dextrins are used for a variety of industrial applications and their desired characteristics change accordingly. For example, canary dextrins are typically used at high solids, between 1:1.25 to 1:0.75 starch:water ratios or 44.4% to 57.1% solids, to give low viscosity dispersions that make them useful in many application areas. While these qualities are desired in many application areas, there are some applications which require relatively lower solids relationships. For example, a usage level at between 1:4.5 to 1:1 starch/ water ratios or 18.1% to 50% solids may be desired. Such compositions made using dextrinization methods known in the art can result in higher viscosity. However, this is done at the sacrifice of solubility and solution stability. Currently, if a high viscosity canary dextrin is produced, it would gain some of the characteristics of a British gum dextrin: that is, the dextrin would be less than 100% soluble in water and not as hydratable.
None of the pyrodextrins currently known in the art are characterized by the specific combination of properties of a relatively high viscosity such as a British gum, 100% solubility In ambient water and solution stable such as a canary dextrin, and high hydratability at ambient temperatures. Typically, high viscosity pyrodextrins never fully hydrate or go into solutions containing limited free water, such as a 60% sucrose solution, without heating. Such properties would be desirable in many applications, particularly in the preparation of confections.
Surprisingly, it has now been discovered that pyrodextrins may be produced which are highly water soluble, and hydratable in a solution which has low free water, at ambient temperature, are viscous relative to a canary dextrin, and are solution stable. These pyrodextrins are produced by drying the starch such that it is substantially anhydrous and effectively removing all the free water in the system.